High contrast stereoscopic projection system

ABSTRACT

A stereoscopic projection system is provided having two channels, each having two LCOS imagers that modulate light on a pixel-by pixel basis. A first polarizing beam splitter is configured to direct light of a first polarization onto a first channel first stage LCOS imager and direct light of a second polarization, opposite the first polarization, onto a second channel first stage LCOS imager. A relay lens system directs the output of the first stage imagers into a second polarizing beam splitter. The second polarizing beam splitter is configured to direct light of the second polarization onto the first channel second stage LCOS imager and direct light of the first polarization onto the second channel second stage LCOS imager.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/430,896 (Atty. Docket No. PU020472), entitled“HIGH CONTRAST STEREOSCOPIC PROJECTION SYSTEM”, filed Dec. 4, 2002,which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to optical projection systemsand more particularly to a high contrast stereoscopic projection system.

BACKGROUND OF THE INVENTION

Liquid crystal displays (LCDs), and particularly liquid crystal onsilicon (LCOS) systems using a reflective light engine or imager, arebecoming increasingly prevalent in imaging devices such as rearprojection television (RPTV). In an LCOS system, projected light ispolarized by a polarizing beam splitter (PBS) and directed onto a LCOSimager or light engine comprising a matrix of pixels. Throughout thisspecification, and consistent with the practice of the relevant art, theterm pixel is used to designate a small area or dot of an image, thecorresponding portion of a light transmission, and the portion of animager producing that light transmission.

Each pixel of the imager modulates the light incident on it according toa gray-scale factor input to the imager or light engine to form a matrixof discrete modulated light signals or pixels. The matrix of modulatedlight signals is reflected or output from the imager and directed to asystem of projection lenses which project the modulated light onto adisplay screen, combining the pixels of light to form a viewable image.In this system, the gray-scale variation from pixel to pixel is limitedby the number of bits used to process the image signal. The contrastratio from bright state (i.e., maximum light) to dark state (minimumlight) is limited by the leakage of light in the imager.

One of the major disadvantages of existing LCOS systems is thedifficulty in reducing the amount of light in the dark state, and theresulting difficulty in providing outstanding contrast ratios. This is,in part, due to the leakage of light, inherent in LCOS systems.

In addition, since the input is a fixed number of bits (e.g., 8, 10,etc.), which must describe the full scale of light, there tend to bevery few bits available to describe subtle differences in darker areasof the picture. This can lead to contouring artifacts.

One approach to enhance contrast in LCOS in the dark state is to use aCOLORSWITCH™ or similar device to scale the entire picture based uponthe maximum value in that particular frame. This improves some pictures,but does little for pictures that contain high and low light levels.Other attempts to solve the problem have been directed to making betterimagers, etc. but these are at best incremental improvements.

Stereoscopic projection systems are used, for example, in 3D theaters tocreate a three-dimensional image by providing different, oppositelypolarized images to the eyes of a viewer. In LCOS imager systems,polarized light must be provided to the LCOS imager for modulation. Theoppositely polarized light is typically not used. Instead it is directedaway from the projection path.

What is needed is a stereoscopic projection system that enhances thecontrast ratio for video images, particularly in the dark state, andreduces contouring artifacts.

SUMMARY OF THE INVENTION

The present invention provides a stereoscopic projection system thatutilizes both of the oppositely polarized light signals, enhances thecontrast ratio for video images, particularly in the dark state, andreduces contouring artifacts. The stereoscopic projection system,comprises two channels, each having two LCOS imagers that modulate lighton a pixel-by pixel basis. A first polarizing beam splitter isconfigured to direct light of a first polarization onto the firstchannel first stage LCOS imager and direct light of a secondpolarization, opposite the first polarization, onto the second channelfirst stage LCOS imager. A relay lens system directs the output of thefirst stage imagers into a second polarizing beam splitter. The secondpolarizing beam splitter is configured to direct light of the secondpolarization onto the first channel second stage LCOS imager and directlight of the first polarization onto the second channel second stageLCOS imager. Since both polarizations of light are used throughout thestereoscopic projection system greater illumination efficiency may beachieved. Because each channel is modulated in two stages, greatercontrast and addressing depth may be achieved.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to the accompanyingfigures, in which:

FIG. 1 shows a block diagram of a stereoscopic projection systemaccording to an exemplary embodiment of the present invention; and

FIG. 2 shows the two-stage modulation of two oppositely polarizedchannels by the stereoscopic projection system of FIG. 1 according to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a two stage stereoscopic projectionsystem. In an exemplary embodiment of the present invention, illustratedin FIG. 1, a two stage stereoscopic projection system comprises twofirst stage imagers 10, 20 and two second stage imagers 30, 40. Thefirst stage imagers 10, 20 comprise a first channel first stage imager10 and a second channel first stage imager 20, which are positionedproximate a first polarizing beam splitter 60 to receive oppositelypolarized light beams and configured to modulate the polarized lightbeams to provide matrices of polarized light pixels. The second stageimagers 30, 40 comprise a first channel second stage imager 30 and asecond channel second stage imager 40 positioned proximate a secondpolarizing beam splitter 70, and used to boost the contrast of thematrices of polarized light pixels from the corresponding first stageimagers 10, 20 by dynamically modulating each polarization or channel asecond time, thereby controlling the black state with an additionalimager. Thus, the projection system illustrated in FIG. 1,simultaneously takes advantage of a high contrast, depth of addressing,polarization recovery and 3D visualization.

In the exemplary projection system illustrated in FIG. 1, anillumination system 2 provides randomly polarized light to the firstpolarizing beam splitter 60. The illumination system 2 comprises a lamp(not shown), which emits light, an integrator (not shown), such as alight pipe or fly eye lens, which collects the light emitted by the lampand directs the light toward the first polarizing beam splitter 60, asystem for scrolling colors or for field sequential color generation(not shown), and a relay lens (not shown)for projecting theillumination.

Randomly polarized light 3 (shown in FIG. 2) from the illuminationsystem 2, enters a first face 61 of the polarizing beam splitter 60. Therandomly polarized light is polarized by a polarizing surface 62 of thefirst polarizing beam splitter 60 into a beam of s-polarized light 7(shown in FIG. 2) and a beam of p-polarized light 5 (shown in FIG. 2).The beam of s-polarized light 7 is deflected through a second face 63 ofthe first polarizing beam splitter 60 and onto a first channel firststage LCOS imager 10. The first channel first stage LCOS imager 10comprises a matrix of pixels that individually modulate the lightincident upon them according to a gray scale value provided to theimager for that pixel. The light incident upon the imager is rotatedninety degrees and reflected by the imager. Thus, the first channelfirst stage LCOS imager directs a first channel matrix of modulatedlight pixels 15 (shown in FIG. 2), comprising p-polarized light backthrough the second face 63 of the first polarizing beam splitter 60. Thefirst channel matrix of modulated pixels 15 then passes through thepolarizing surface 62 and fourth face 65 of the first polarizing beamsplitter 60.

The beam of p-polarized light 5 passes through the polarizing surface 62and a third face 64, and onto a second channel first stage LCOS imager20. The second channel first stage LCOS imager 20 also comprises amatrix of pixels that individually modulate the light incident upon themaccording to a gray scale value provided to the imager for that pixel.The light incident upon the imager is rotated ninety degrees andreflected by the imager. Thus, the second channel first stage LCOSimager 20 directs a second channel matrix of modulated light pixels 25(shown in FIG. 2), comprising s-polarized light back through the thirdface 64 of the first polarizing beam splitter 60. The s-polarized secondchannel matrix of modulated light pixels 25 is then deflected bypolarizing surface 62 through the fourth face 65 of the first polarizingbeam splitter 60.

The first channel matrix of modulated pixels 15 and the second channelmatrix of modulated light pixels 25 are simultaneously focused by arelay lens system 80 configured to focus the matrices of modulated lightpixels from the first stage imagers on a pixel-by-pixel basis onto thecorresponding pixels of the second stage imagers. The relay lens systemprovides a magnification of about −1 and a highly ensquared energy,whereby a large percentage of the light energy from a particular pixelin a first stage imager 10, 20 is ensquared within a square area of thecorresponding pixel of a second stage imager. In an exemplaryembodiment, this relay lens system 80 comprises a double-gauss lens set,which is preferably symmetrical, and consists of a pair of asphricalacrylic lenses 81, 85 surrounding a pair of glass acromatic lens 82, 84,with a lens stop 83 between the acromatic lenses. Suitable lens surfacescan be developed using ZEMAX™ software. An exemplary lens system isdescribed in U.S. Patent Application (Attorney Docket No. PU020473),which is incorporated herein by reference.

The relay lens system 80 is configured to focus the matrices ofmodulated light pixels 15, 25 from the first stage imagers 10, 20 on apixel-by-pixel basis onto the corresponding pixels of the second stageimagers 30, 40, through the second polarizing beam splitter 70. Lenssystem 80 is accordingly positioned between the first polarizing beamsplitter 60 and the second polarizing beam splitter 70.

First channel modulated matrix of light pixels 15 enters secondpolarizing beam splitter 70, through first face 71, and because it isp-polarized light, it passes through polarizing surface 72 and secondface 73 onto first channel second stage LCOS imager 30. First channelsecond stage LCOS imager 30 comprises a matrix of pixels thatindividually modulate the light incident upon them according to a grayscale value provided to the imager for that pixel. The light incidentupon the imager is rotated ninety degrees and reflected by the imager.Thus, the first channel second stage LCOS imager 30 directs a firstchannel matrix of twice modulated light pixels 35 (shown in FIG. 2),comprising s-polarized light back through the second face 73 of secondpolarizing beam splitter 70. The first channel matrix of twice modulatedpixels 35 is then deflected by polarizing surface 72 through fourth face75 of the second polarizing beam splitter 70.

Because the output of each pixel of the first channel first stage LCOSimager 10 is focused onto a corresponding pixel of the first channelsecond stage imager 30, the output of each pixel of the first channelsecond stage imager 30 is twice modulated, once by the first channelfirst stage LCOS imager 10 and again by the first channel second stageimager 30. The advantage of the combination of a first stage imager anda second stage imager is that it boosts the contrast of the channel. Ifthe contrast using one imager and the optical system used around theimager was c, than using a two stage system results in a contrast of c².Another advantage is that if the depth of addressing for one imager is 8bits, using two imagers results in the advantage of getting 16 bitlevels for addressing, hence improving the contouring and further imageprocessing.

Second channel modulated matrix of light pixels 25 enters the secondpolarizing beam splitter 70, through first face 71, and because it iss-polarized light, it is deflected by polarizing surface 72 throughthird face 74 onto second channel second stage LCOS imager 40. Secondchannel second stage LCOS imager 30 comprises a matrix of pixels thatindividually modulate the light incident upon them according to a grayscale value provided to the imager for that pixel. The light incidentupon the imager is rotated ninety degrees and reflected by the imager.Thus, the second channel second stage LCOS imager 40 directs a secondchannel matrix of twice modulated light pixels 45 (shown in FIG. 2),comprising p-polarized light back through the third face 74 of secondpolarizing beam splitter 70. The second channel matrix of twicemodulated pixels 45 then passes through the polarizing surface 72 andfourth face 75 of the second polarizing beam splitter 70.

As with the first channel, the output of each pixel of the secondchannel first stage LCOS imager 20 is focused onto a corresponding pixelof the second channel second stage imager 40. Thus, the output of eachpixel of the second channel second stage imager 40 is twice modulated,once by the second channel first stage LCOS imager 20 and again by thesecond channel second stage imager 40.

In one exemplary embodiment of the invention, first channel imagers 10,30 are addressed with the same video signals as second channel imagers20, 40. Thus, the second polarity light beam from the first polarizingbeam splitter 60 is recycled by the second channel, and the intensity orbrightness of the viewable image is about twice the level of a viewableimage of a single channel two-stage projection system, in which onepolarization of light is not used. In this embodiment, the life of thelamp can be increased, because less light is required from the lamp inorder to achieve the same level of light in the viewable image due tothe recycling of the second channel or polarity of light.

In an alternate embodiment of the invention, the first channel imagers10, 30 are addressed with a first video signal intended for a first eyeof a viewer, and the second channel imagers 20, 40 are addressed with asecond video signal intended for a second eye of the viewer. The matrixof twice modulated first channel pixels of light 35 and the matrix oftwice modulated second channel pixels of light 45 are projected on ascreen (not shown) by projection lens system 4 with orthogonalpolarizations. A three dimensional (3D) viewing system is provided whereone channel is addressed with the video signal intended for one eye,while the other channel is addressed with the video signal intended forthe second eye. Polarization goggles worn by the viewer select the rightimage for each eye resulting in stereoscopic viewing.

The present invention provides several advantages. Very high contrastand addressing depth are provided by the two stages of imagers for eachchannel. Light efficiency may be provided through polarization recyclingby the additional channel. 3D capability can be provided by addressingthe first channel imagers and the second channel imagers with differentvideo signals intended for the different eyes of a viewer. Also, otherthan the imagers, the first channel and the second channel can utilizethe same components (i.e., illumination system, polarizing beamsplitters, relay lens system, and projection lens system) providingstereoscopic projection with minimal parts.

The foregoing illustrates some of the possibilities for practicing theinvention. Many other embodiments are possible within the scope andspirit of the invention. For example, first channel imagers 10, 30 ofthe exemplary embodiment illustrated in FIGS. 1 and 2 and describedabove receive p-polarized light and s-polarized light respectively andthe second channel imagers 20,40 receive s-polarized light andp-polarized light respectively. However, the polarizations may bereversed within the scope of the present invention by exchanging thepositions of the imagers. It is, therefore, intended that the foregoingdescription be regarded as illustrative rather than limiting, and thatthe scope of the invention is given by the appended claims together withtheir full range of equivalents.

1. A stereoscopic projection system, comprising: a first channel firststage imager and a second channel first stage imager, each configured tomodulate polarized light input on a pixel-by-pixel basis proportional togray scale values provided to each pixel of the imager, rotate thepolarization of the light and reflect a matrix of modulated lightpixels; a first channel second stage imager and a second channel secondstage imager, each configured to modulate a matrix of modulated pixelsof light on a pixel-by-pixel basis proportional to gray scale valuesprovided to each pixel of the imager, rotate the polarization of thelight and reflect a matrix of twice modulated light pixels; a relay lenssystem configured to focus the matrices of modulated light pixels fromthe first stage imagers on a pixel-by-pixel basis onto the correspondingpixels of the second stage imagers; a first polarizing beam splitterconfigured to polarize light input into oppositely polarized lightinputs, direct the oppositely polarized light inputs onto the firstchannel first stage imager and the second channel first stage imagerrespectively, and direct the matrices of modulated light pixels from thea first channel first stage imager and a second channel first stageimager into the relay lens system; and a second polarizing beam splitterconfigured to direct the oppositely polarized matrices of modulatedlight pixels from the first channel first stage imager and secondchannel first stage imager onto the first channel second stage imagerand the second channel second stage imager respectively, and direct thematrices of twice modulated light pixels from the second stage imagersinto a projection lens system.
 2. The stereoscopic projection system ofclaim 1 wherein the first channel imagers and the second channel imagersare addressed with the same signal to enhance the brightness andcontrast of the stereoscopic projection system.
 3. The stereoscopicprojection system of claim 1 wherein the first channel imagers areaddressed with the video signal intended for a first eye of a viewer andthe second channel imagers are addressed with the video signal intendedfor a second eye of the viewer to provide a three dimensional image. 4.The stereoscopic projection system of claim 3 further comprisingoppositely polarizing lenses configured for viewing the images from thefirst channel and the second channel.
 5. The stereoscopic projectionsystem of claim 1 wherein the relay lens system comprises a double-gaussrelay lens set.
 6. A stereoscopic projection system, comprising: a firstchannel, having a first stage LCOS imager and a second stage LCOSimager; second channel having a first stage LCOS imager and a secondstage LCOS imager; a first polarizing beam splitter configured to directlight of a first polarization onto the first channel first stage LCOSimager and direct light of a second polarization, opposite the firstpolarization, onto the second channel first stage LCOS imager; and asecond polarizing beam splitter configured to direct light of the secondpolarization onto the first channel second stage LCOS imager and directlight of the first polarization onto the second channel second stageLCOS imager.
 7. The stereoscopic projection system of claim 6 whereinthe first channel LCOS imagers and the second channel LCOS imagers areaddressed with the same video signals to project a common image withenhanced light intensity.
 8. The stereoscopic projection system of claim6 wherein the first channel LCOS imagers and the second channel LCOSimagers are addressed with different video signals to providestereoscopic viewing.
 9. The stereoscopic projection system of claim 6further comprising a relay lens system that directs the output of boththe first stage LCOS imagers onto the second stage LCOS imagers on apixel-by-pixel basis.
 10. The stereoscopic projection system of claim 9wherein the relay lens system comprises a double-gauss relay lens set.11. The stereoscopic projection system of claim 9 further comprising aprojection lens for projecting both the first channel image and thesecond channel image onto a viewing screen.
 12. The stereoscopicprojection system of claim 11 further comprising an illumination systemproviding random polarity light to the first polarizing beam splitter.